VISCOSITY 



229 



tion of casein and that the volume of these particles is regulated 

 by the Donnan equilibrium. 



6. These experiments leave little doubt that the high viscosity 

 of certain protein solutions, such as gelatin or casein, is due to the 

 existence of solid particles occluding large quantities of water, 

 the amount of which is regulated by the Donnan equilibrium, 

 while the isolated ions of proteins in solution or the particles too 

 small to occlude water have no share in the causation of high 

 viscosities. 



in solutions. 



The quantities of water which can be occluded in a solid jelly 

 of gelatin are enormous. If we assume the molecular weight 

 of gelatin to be of the order of magnitude of about 12,000, a 

 solid gel of 1 per cent originally isoelectric gelatin contains over 

 60,000 molecules of water to 1 molecule of gelatin. It is out of 

 the question that such masses of water could be held by the 

 secondary valency forces of the gelatin and water molecules. 

 Casein particles occlude much less water and for this reason the 



